The storage of liquefied hydrogen presents numerous advantages and, in particular, the relative ease with which liquid hydrogen can be compressed. Indeed compressing liquid hydrogen costs less in terms of compression than compressing hydrogen gas. This is notably because it is less costly in terms of energy expenditure to compress a volume of liquid than to compress a volume of gas.
Generating a high pressure using a pump for liquid hydrogen reduces the energy consumption of a refueling system by a factor of about five as compared with an equivalent system using a gas compressor.
The evaporative losses of liquid hydrogen in a cryogenic pump such as this may be substantial if the pump is not being used optimally. This liquid hydrogen is removed from the compression chamber before being pumped, so that the fluid drawn into the pumping cylinder is not a biphasic mixture which would lower the efficiency of the pump designed to pump only liquid. The evaporative hydrogen gas has therefore to be removed at relatively low pressure (intake pressure).
Because these evaporative losses are impossible to eliminate, a cryogenic pump will always generate a degassing delivery corresponding to an evaporation of cryogenic liquid within the pump housing.
This purge of hydrogen gas is mostly discharged to the atmosphere or recompressed using a gas compressor, but so doing is not satisfactory in terms of the energy balance sheet and makes the plant more complicated.
It is an object of the present invention to alleviate all or some of the abovementioned disadvantages of the prior art.